Concern at new blood-thinning drug

Doctors appear not to have been adequately advised on how to prescribe a blood-thinning drug which has attracted attention for possible safety issues, Prof Stephen Duffull, of the University of Otago's School of Pharmacy, says.

Pharmac fully funded dabigatran, branded as Pradaxa, in July as an alternative to warfarin. A Pharmac-appointed haematologist group monitoring the drug reported 36 bleeds, while the Dunedin-based Centre for Adverse Reactions Monitoring has received about 50 reports of bleeds, including two in Otago and Southland.

The blood-thinning drug is used to prevent strokes in those with heartbeat rhythm issues, and is used for patients undergoing orthopaedic surgery.

Unlike warfarin it does not require patients to undergo constant testing for effects.

The haematologists' report revealed some doctors had incorrectly prescribed the drug for patients for whom it was known to be unsuitable, such as those with kidney problems.

Prof Duffull said doctors had been reminded of prescribing rules which should prevent some of the adverse reactions, but it was questionable whether this was prompt enough.

He took issue with Medsafe guidelines indicating two doses.

He believed individualised dosing could be as important for dabigatran as for warfarin, which is known for its tight safety window for dosage.

Dosage was all-important for a drug affecting a highly complicated bodily process; it was "not like prescribing Panadol".

Unlike warfarin, the new drug did not have an antidote, making bleeds more dangerous.

Dabigatran was not the "panacea" many hoped; there was too much expected of new drugs.

Often old drugs were as safe and effective as new ones, he said.

Pharmac medical director Dr Peter Moodie rejected the suggestion dabigatran was as dose-sensitive as warfarin. Clinical trial data indicated it was safe and effective at the two recommended doses.

All drugs carried risk, and given the patient group was largely elderly, he advised caution in attributing blame for adverse events.

Doctors had been adequately advised of prescribing protocols, such as who the drug was suitable for, he said.

For some patients who had not tolerated warfarin well the drug was a major improvement.

Medsafe said it was closely monitoring the drug for safety but was satisfied its benefits outweighed its risks.

- eileen.goodwin@odt.co.nz